Exothermic reactions Homogeneous mixture

These results can be explained by considering that at this 02 CH4 ratio the homogeneous combustion reaction is not favored and consequently the feed mixture reacts in the catalytic section where the heat developed by the exothermic reactions is responsible for the remarkable temperature increase. 

Pressure-Temperature Explosion Limit for Mixtures of Constant Compositior. Consider a gaseous, homogeneous, simple ordered, exothermic reaction occurring in a closed vessel. The vessel is assumed to be immersed in a furnace so that the vessel walls always remain at the furnace temperature T0. For the reaction mA + nB —> products, with an overall reaction order N = m + n, the reaction rate, r, is given by r = kCAmCBn, where Ca and Cb, are concentrations of the reactants, A and B. The specific rate constant, k, is assumed to obey the simple Arrhenius relation, k = Cc EIRT, where C, the pre-exponential factor, is independent of the absolute temperature, T R is the molar gas constant and E is the energy of activation. The initial reactant concentrations, (Ca)0 and (CB)a, are given in terms of P, the initial total pressure XQ, the initial mole fraction of A, and T0, the initial temperature of the reactant mixture, as follows ... 

Ionic liquids should also be very suitable for use as monopropellants, but the salts used must contain either the oxidizer and fuel combined, or salt mixtures which contain both oxidizing and reducing salts. Since these mixtures are homogeneous systems which contain both the oxidizer and fuel, they can be labeled as monopropellants, just as hydrazine is. Particularly interesting are salt mixtures which are less toxic and have a lower vapor pressure than hydrazine. Such mixtures are also known as green propellants . Suitable anions are the nitrate or dinitramide ions [58], A combination which has already been studied intensively as an oxidizer is the HAN, hydroxylammonium nitrate system. ADN, ammonium nitrate (AN) and hydrazinium nitrate (HN) have also been investigated. As fuels, hydroxylammonium azide (HAA), ammonium azide (AA) or hydrazinium azide (HA) may be appropriate. As a rule, these salt mixtures are not used as pure substances on safety grounds, but with 20 or 40% water added they then decompose catalytically in an exothermic reaction. Table 9.7 shows the dependence of the calculated specific impulses on the water content for such salt mixtures. 

Several preparative methods have been described for iodotrimethylsilane. Of these the reaction of hexamethyldisilane with iodine looks cleanest. A mixture of hexamethyldisi-lane (0.3 g, 2 mmol) and iodine (0.5 g, 2 mmol) is heated at ca 65 °C in a 20-mL flask fitted with a reflux condenser an exothermic reaction occurs and a homogeneous solution is formed. The mixture is then heated under reflux for 1.5 h. At this stage, hexamethyldisilane is converted quantitatively to iodotrimethylsilane (confirmed by NMR). 

Reaction, Work-Up, and Isolation Transfer the crude A-acetamidobenzenesulfonyl chloride obtained in the previous experiment to the Erlenmeyer flask, and add 15 mb of concentrated (28%) ammonium hydroxide. A rapid exothermic reaction may occur if the crude 4-acetamidobenzenesulfonyl chloride contains acidic contaminants that were not removed by the aqueous washings in the previous step. Use a stirring rod to break up any lumps of solid that may remain the reaction mixture should be thick but homogeneous. Heat the mixture at 70-80 C for about 0.5 h. Cool the reaction mixture in an ice-water bath and collect the product by vacuum filtration. Wash the crystals with cold water and air-dry them. ... 

Thermal sensitivity data are now primarily obtained using the thermal analysis method of differential scanning calorimetry (DSC) (see Chapter 2). Thermal sensitivity is the most reproducible, and best understood, of the various types of sensitivity tests, owing to the relatively minor effect of the specific test conditions on the value that is obtained. Thermal sensitivity is the result of the chemistry that occurs in a given mixture upon heating, and it is relatively independent of factors such as homogeneity, particle size, and percent composition. It can be very dependent, however, on the addition or omission of a component in a particular composition, especially if that component plays a role in the initial exothermic reaction that occurs upon heating of the material. 

In reactive distillation, both the chemical reaction and the distillative separation of the product mixture are carried out simultaneously. This integrative strategy allows us to overcome chemical equilibrium limitations. For an exothermic reaction, the heat of reaction can be used directly for distillation. The term catalytic distillation is also used for such systems where a catalyst (homogeneous or heterogeneous) is used to accelerate the reaction. The synthesis of methyl acetate and MTBE (methyl tertiary butyl ether) are the two most prominent examples, where reactive distillation is used on an industrial scale (for MTBE see Section 4.10.8.1). It is beyond the scope of this textbook to discuss more details of this technology. Details can be found in the literature (Sundmacher and Kienle, 2002 Harmsen, 2007 Taylor and Krishna, 2000 Krishna, 2002 Stankiewicz, 2003). 

Isolation of (I-l) and (I-m). a) 3,6,17-Triacetylnormorphine (I-l). Morphine N-oxide (10 mg) was heated at reflux temperature in 5 ml acetic anhydride- e for one hour. In the first several minutes of the reaction, the solution appeared exothermic with simultaneous color changes (yellow to red to light brown). The solution was then cooled to room temperature, and water (10 ml) was added. When the mixture became homogeneous, solid sodium carbonate was added to pH 9.0. The mixture was extracted with 3x125 ml portions of ether.The extracts were combined and evaporated to dryness. The ether extract was mixed till homogeneous with 8g celite, 10 ml 1% perchloric acid and 10 ml ether to comprise the top layer of a partition column (2.5 in. diam.). The bottom layer of the column consisted of a homogeneous mixture of celite (5 g) and 10 ml 1% perchloric acid. The column was eluted with 300 ml anhydrous ether. The ether eluate was evaporated to dryness. GC/MS analysis indicated the presence of (j[-i) (M at m/e 397). GC quantitation established its purity as 94.7%. Elution of the celite column with 300 ml water-washed chloroform followed. The chloroform eluate was evaporated to dryness and analyzed by GC/MS. The major constituent was heroin (M at m/e 369), as well as several other minor products, b) 3,6,17-Triacetyl-dQ normorphine (I-m). Morphine N-oxide (10 mg) was dissolved in 5 ml acetic anhydride- 0 and heated at reflux temperature for one hour. The reaction mixture was worked up by the procedure described above for 3,6,17-jriacetylnormorphine (1 -1). 3,6,17-Triacety 1-dq-nor-morphine (M at m/e 406) was obtained in the ether eluate from a 1% perchloric acid-celite column and was analyzed by GC/MS. T e major constituent from the chloroform eluate was heroin- 0 (M at m/e 375). 

Acetyl chloride (35 g, 0.45 mol) was added dropwise to a slurry of octamethyltrisilane (40 g, 0.20 mol) and aluminum chloride (53 g, 0.40 mol) with stirring. A moderate exothermic reaction took place, and finally the mixture became homogeneous. After the addition was completed, the mixture was stirred for 2 h. The product was simply removed from the mixture by distillation under reduced pressiue. After fractionation through a 25-cm column packed with glass helicoils, l,3-dichloro-l,l,2,2,3,3-hexamethyltrisilane (40 g, 84%) was obtained as a colorless pure liquid. Bp 89°C/14 mmHg. 

In homogeneous process the components of the reaction mixture are mutually soluble including a homogeneous catalysts if used. Mixing of reactants is necessary if the process to be carried out either (1) consists of a series of reactions of which the rates differ significantly and at least one of the important reactions is very fast, or (2) is exothermic and fast enough to produce problems with removal of heat from the reaction zone to the surroundings. 

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